Eshell

Eshell is a shell-like command interpreter implemented in Emacs Lisp.
It invokes no external processes except for those requested by the
user. It is intended to be an alternative to the IELM (see Emacs Lisp Interaction)
REPL for Emacs and with an interface similar to command shells
such as bash, zsh, rc, or
4dos.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with the Front-Cover Texts being “A GNU Manual”,
and with the Back-Cover Texts as in (a) below. A copy of the license
is included in the section entitled “GNU Free Documentation License”.

(a) The FSF's Back-Cover Text is: “You have the freedom to copy and
modify this GNU manual.”